The purpose of the proposed research program is to define the molecular structure, genetic organization and regulatory function of the Drosophila Y chromosome during spermatogenesis. Initial studies will be directed toward the development of a method of Y chromosome isolation; subsequent characterization of Y chromosomal DNA sequences will be accomplished by DNA/DNA hybridization techniques. Genetic analysis will utilize the detection and recovery of temperature-sensitive sterile mutations which will then be subjected to cytogenetic anlaysis as a measure of Y chromosomal activity during spermatogenesis. Biochemical assay of spermiogenesis will qualitatively and quantitatively describe testicular macromolecular biosynthesis in vitro.